> On Sun, Sep 29, 2013 at 11:25:36PM +0800, Anand Jain wrote:
>> It needs a lot more information about the snapshots if
>> snapshot's life cycle has to be all auto managed by
>> scripts _some day_. this patch is a step towards that.
>>
>> This patch provides the size which would be freed
>> if the subvol/snapshot is deleted.
>> preview:
>> ---------------------
>> btrfs su show /btrfs/sv1
>> ::
>> Unshared space: 89.09MiB
>
> Useful information, but it takes time to calculate the number. The tree
> search ioctl has significant overhead and seeking all over the extent
> tree can be also lengthy. I've tried it on a random subvolume on a SSD
> disk and it's been running 10 minutes already, one cpu is at 100%.
No wonder Anand's approach is inefficient.In Anand's approach:
Search Every EXTENT_DATA
Search every extent's refs in extent tree.
If we want to speed up this progress, i think we can split it into two parts:
1. First to search inline extent_data
2. Secondly search in extent tree to calculate (extent refs=1)
This will avoid n*n rather than n+n which is better…
Thanks,
Wang
>
> david
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